Lmmobilization And Durability Of Zircon Synthesized By High Sintering

In order to investigate the capability and chemical stability of zircon immobilizing Pu （Ⅳ） and U（Ⅴ）, Nd³⁺ and Ce⁴⁺ was used as the simulacrum for Pu （Ⅳ） and U（Ⅴ） respectively. The samples of Zr_2-xNd_xSi₂O_8-o.5x（0.01≤x≤0.1） and Zr_1-xCe_xSiO₄ （0≤x≤0.1） were synthesized by solid-state reaction at high temperature in this thesis. The solution law of simulative nuclides in zircon, the preparation technology of sample and the changes of phases, structures, microstructures, destiny and expansion rate were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and the Fullprof structural refinement method, and so on. The experiment was carried out at a temperature of 1823K and 72h duration time.The results indicate that single phase of zircon was synthesized successfully and with a high synthesis rate; The cell parameter （a,b,c）,unit cell volume and the destiny of sample have a positive linear correlation with the amount of simulation nuclides while the volume of sample is on the contrary; A clearly grain boundary,grain size was about 5 μm and was arranged in a blocklike.The chemical durability of Zr_2-xNd_xSi₂O_8-o.5x（0.01≤x≤0.1） and Zr_1-xCe_xSiO₄ （0≤x≤0.1） ceramic waste-forms sintered by high temperature under the action of multiple environments was researched by MCC static leaching using the hydrothermal reaction still as the leaching device for simulating the environment of geologic disposal. The results show that the Zircon ceramic waste-form prepared by high temperature shows excellent chemical durability under the action of multiple environments (leaching temperature of 40、90、150 ℃, leaching pressure of leaching agent pH of （4、6.7、10）. When at a certain temperature, leaching concentration of Nd³⁺ and Ce⁴⁺ are the biggest in acid leaching while leaching concentration of Nd³⁺ and Ce⁴⁺ is minimal in deionized water leaching. When leaching agent pH must, with the temperature lowering Nd³⁺ and Ce⁴⁺ leaching concentration decreases gradually. In the leaching cycle, with the extension of time, the Nd³⁺ and Ce⁴⁺ leaching concentration gradually reduced to a lower concentration and then keep stable.